Yogo's Curse Edit
In 39, during the War Against Fu Leng, the Phoenix Clan shugenja Asako Yogo, who was Asako's husband, won a great victory against Fu Leng's maho tsukai troops. However, shortly before the defeat, one of the maho tsukai placed a powerful curse on Yogo. 
The Phoenix recognized the black magics fouling Yogo's chi, but despite their best efforts, their limited knowledge of maho was not enough to remove the curse. However, they were able to identify it. Yogo was destined (at the most crucial moment of his life) to betray the one he loved the most. The Phoenix shugenja also determined that the curse would pass on thorugh his blood to his children, his descendants and all others who bore his name. Yogo left the Phoenix and joined the Scorpion Clan after Bayushi convinced him to do it, and founded the Yogo family. 
All members of the Yogo family were born with this powerful curse that invariably ended with the betrayal of the person that he or she loved most. The Yogo Curse stroke each family individual exactly once, and though it could not be detected by outsiders, a Yogo always knew when his curse had been fulfilled. Some betrayals were more dramatic than others and, some Yogo were fortunate enough to fulfill their curse early in life. Examples of this were the following: accidentally destroying a cherished family heirloom, stumbling over a phrase in a loved one's funeral ceremony, injuring a sibling during training, etc.). 
The longer it took for a person to fulfill their curse and the more they tried to prevent it, the worse it was when it finally came to pass. The leadership of the Yogo family was careful to watch their charges and kept a close watch on those who had not yet fulfilled their curses. 
The Curse in the Scorpion Clan Edit
All members of the Yogo family were born with a powerful curse that invariably ended with the betrayal of their family. The Yogo took a strange, macabre joy in fulfilling their curses, especially if they were lucky enough to do so in a harmless manner. When a child broke his curse early, his family celebrated, inviting friends and family for miles around. Fulfillment of the curse was a joy; as the Yogo could now be fully trusted.
Yogo were always warned never to try to break their curse intentionally. The curse's true nature was to bring pain and misery to the Yogo family, so harmless fulfillments seemed accidental more than anything else. Those who tried to break the curse often draw the wrath of angry kansen spirits, causing the curse to break in a manner that caused pain and misery to the entire family.
Because of the Curse, the Yogo were forbidden to marry within the Scorpion Clan.  However, Yogo samurai had married secretly inside the clan for centuries. Other Scorpion could inherit the Curse if they had Yogo ancestors, although it was not guranteed. 
A side effect of the Yogo Curse was that an individual instinctively knew when they had fulfilled the Curse's terms, so he was fully aware of the depth and breadth of his betrayal. 
The Curse & the Asako Edit
In addition to the Yogo family, occasionally a member of the Asako family, also descendants of Yogo, would manifest a close enough relation to the once-husband of their family's namesake that they would receive a share of his curse. The Asako, as a result, also remained aware of the lingering curse and its effect on their family.